1. Technical Field
This invention relates to the art of making engine housings and combustion chambers for internal combustion engines and, more particularly, to the art of making a unitary block for the combustion chamber, sometimes referred to as a monoblock.
2. Description of the Prior Art
There has been a longstanding need and desire to make cylinder blocks and heads for internal combustion engines out of materials lighter than the traditional cast iron. One of the earliest and best-known commercial attempts to reduce weight of the engine was the use of an all-aluminum cylinder block (see SAE 710150 "Vega 2300" by Reuss and Hughes, 1971, page 22). To increase the wear resistance of the cylinder bore surface of the Vega block, a special high-silicon alloy was employed which required etching of the bore surface to expose silicon particles for the enhancement of wear resistance when working against pistons.
Other attempts at the deployment of aluminum in the housing of internal combustion engines have included the use of cast-in-place iron liners suited for the use of aluminum pistons and accompanied by the use of separate cast iron heads (see SAE 307C "Chrysler Corporation's Die-Cast Aluminum Slant 6 Engine", by Moeller et al, 1961, pages 5-11). Again, this disclosure was limited by the use of separate heads and blocks, requiring reinforcing means to join the members together at a gasketed parting plane.
Monoblock engine designs have been envisioned to eliminate such weight increases resulting from reinforcement to join separate head and blocks, and to better control the thermal gradients in the combustion chamber. No attempt is known which clearly discloses the use of aluminum as the material for the monoblock principal housing, but it can be assumed that in U.S. Pat. Nos. 3,521,613 and 4,252,175 the disclosures of a die casting method for making a monoblock engine may comprehend the use of aluminum. In each of these disclosures, only a thin iron liner is employed as a bearing surface for the reciprocating pistons, with the die-cast material acting as the principal material for defining most of the combustion chamber as well as the exhaust and intake passages. In the first patent, no fluid is used for purposes of cooling the engine since it is designed primarily for small two-stroke engine applications which are presumably air cooled. In the second patent, the cooling chambers are defined totally within the die-cast material, separate and independent from the iron liner.
The inventions of the above patents present significant problems. First, there can be possible delamination of the iron liner from the die-cast material of the cylinder bore, inhibiting heat transfer severely Second, the iron liner prevents direct transfer of combustion heat directly through one material to the cooling medium. As a result, there is a poorer thermal gradient through all of the walls of the engine and such gradient is nonuniform since part of the material in contact with the cooling fluid is aluminum and the other part is a composite of an iron liner and aluminum.
Accordingly, a principal object of this invention is to provide a monoblock construction and method of making same which employs (i) iron as an envelope for substantially all of the hot chambers or zones of the engine, and (ii) aluminum as a jacket. The aluminum jacket desirably should wrap a fluid cooling medium directly in contact with substantially all of the surfaces of the iron member, except for such extremities thereof which are attached to the aluminum jacket at the extremities of the jacket.